The invention relates to breathing apparatuses and methods.
Tracheal gas insufflation (TGI) used in breathing apparatuses combined with mechanical ventilation (MV) through an endotracheal tube results in reduced dead space ventilation, and allows use of lower respiratory rates and tidal volumes at lower peak inspiratory pressures (PIP). In its simplest form, in TGI, a straight catheter with an open tip or side holes delivers a supply of fresh oxygen containing gas to flush out the anatomical dead space. Dead space is determined from the volume of the trachea and tracheostomy or endotracheal tube utilized, which, for example, can be about 120 cc in an adult. The catheter may be introduced into a patient""s trachea either through an endotracheal tube, or percutaneously through a tracheostomy.
One example of a prior art breathing apparatus is provided in U.S. Pat. No. 5,186,167 (hereinafter xe2x80x9cU.S. Pat. No. 5,186,167xe2x80x9d), which discloses a method and apparatus for intratracheal ventilation (ITV) and intratracheal pulmonary ventilation (ITPV) in which a reverse thrust catheter (RTC) positioned in a patient""s trachea at the carina supplies a constant supply of fresh oxygen containing gas to flush anatomical dead space. The catheter includes a catheter tip which directs the constant supply of fresh oxygen containing gas in a manner so as to create sub-atmospheric pressures near the carina and thus allows control of intratracheal airway pressures during the entire respiratory cycle and prevents overinflation of the lungs. The distal end of the catheter preferably includes a diffuser which is positioned at a level near the patient""s carina, and which includes a plurality of gas passage ports along the length thereof. At high gas flow rates through the catheter, which may be ideal for a particular treatment protocol, the pressure created by a stream of fresh air and oxygen may result in some back pressure, which can impair expiration and keep the lungs continuously overinflated. To overcome the problem of back pressure, and to provide a way of controlling intratracheal airway pressures during the entire respiratory cycle, the tip of the catheter is provided with the diffuser, which serves to distribute the fresh air and oxygen into the trachea while eliminating the distal jet effect provided by an open ended catheter. By avoiding the distal jet effect, the use of the diffuser has been found to significantly reduce the distal airway pressures. U.S. Pat. No. 5,186,167 proposes using a tubular portion with a closed distal end at the catheter tip and with an annular opening or gas exit port to provide a controlled low pressure zone near the carina. The gap xe2x80x9caxe2x80x9d of the annular opening or exit port determines the flow-pressure characteristics at the level of the carina for any given gas flow rate, and is disclosed as being small, that is, in the range from 0.005 to 0.020 inch. The disclosure in U.S. Pat. No. 5,186,167 is incorporated herein by reference.
U.S. Pat. No. 5,544,648 pertains to a device for creating a sub-atmospheric pressure near the carina of a subject which includes a channel or perforation for the passage of an oxygen-containing gas therethrough. The channel or perforation is open in a direction distal of the subject so as to establish a zone of sub-atmospheric pressure by reverse venturi effect during patient exhalation. The sub-atmospheric pressure in the zone facilitates removal of carbon dioxide from the lungs of the patient and permits intratracheal and/or intratracheal pulmonary ventilation to be performed at pressures less than those conventionally required for such ventilation. The above device is generally of the type described in U.S. Pat. No. 5,186,167 (i.e.: a RTC). According to U.S. Pat. No. 5,544,648, the device obviates the risks inherent in RTC""s, specifically, the possibility of detachment of a tubular member in those devices, and the possible complications of surgical recovery of the tubular member from the bronchi or lungs of the subject. The device in U.S. Pat. No. 5,544,648 achieves the above by either eliminating the tubular member of prior reverse venturi devices, or by providing a shoulder affirmatively preventing distal movement and loss of it.
In pilot studies in sheep using breathing apparatuses of the prior art, it has been found that the early response after a RTC, such as the one described in U.S. Pat. No. 5,186,167, was introduced percutaneously through a mini-tracheostomy into the trachea of non-intubated awake sheep was similar to what has been observed in intubated sheep (where the catheter is introduced into the trachea of the sheep through an endotracheal tube), namely, a decrease in respiratory rate, lower spontaneous tidal volume and decreased effort of breathing. However, after some minutes to hours, the breathing pattern of the sheep was observed to change, vacillating between a normal pattern and a new, unexpected pattern. In this unexpected pattern, upon spontaneous prolonged closing of the glottis of the sheep (i.e. the voice box of an animal, containing the vocal folds, together with accessory muscles used in phonation), the insufflated gas accumulated within the lungs, passively expanded the same without effort on the part of the sheep. This expansion of the lungs was observed to be eventually relieved by a spontaneous opening of the glottis, leading to expiration. The above unexpected pattern was observed to be marked by measured intrapulmonary airway pressures which were frequently dangerously high.
In this respect, it is noted that the glottis of the sheep is active both during inspiration and expiration, and acts as a valve which opens and closes the trachea and hence the lungs to the surrounding atmosphere. Closing of the glottis prevents loss of air through the mouth and the nose, resulting in inspiration brought about by the introduction of oxygen containing gas into the trachea through the catheter. Given that the total work needed to activate a muscle innervating the glottis (which weighs less than 1 g) is negligible, and given that little or no effort is needed to expand the chest wall or to move the diaphragm, in essence, the potential energy from the compressed gas being introduced into the trachea through the catheter was spent in the above experiment to expand the lungs, expiration remaining passive. However, disadvantageously, as previously described, the expansion of the lungs led to dangerously high pressures existing frequently therein during the respiratory cycle, which pressures were not effectively relieved by a spontaneous opening of the glottis.
It is an object of the invention to overcome the disadvantages associated with the prior art by providing a spontaneous breathing apparatus and method which eliminate the build up of dangerously high pressures in the lungs of a subject during insufflation.
It is another object of the invention to provide a spontaneous breathing apparatus and method which obviate the use of an endotracheal tube, thus eliminating the need for cleaning the tube intermittently. Cleaning the endotracheal tube commonly involves suctioning through external means. The above procedure is not only uncomfortable and cumbersome to the subject, but also increases the risk of introducing bacterial infections, such as nosocomial pneumonia, into the trachea by virtue of the frequent manipulation of the breathing apparatus associated with the endotracheal tube. The spontaneous breathing apparatus according to the invention eliminates the above disadvantages, providing spontaneous, on-line cleaning of mucus from the trachea. Additionally, the elimination of an endotracheal tube from the spontaneous breathing apparatus advantageously decreases the risk of tracheal aspiration, and further does not interfere with swallowing, eating, drinking, speech and cough.
It is a further object of the invention to provide a spontaneous breathing apparatus which includes a catheter configured for promoting mucous flow in a direction outside of the trachea, thus aiding mucociliary transport. This embodiment is capable of controlling intratracheal airway pressures during the respiratory cycle while substantially reducing the risk of tracheal injury from the jet of air emanating from the catheter.
The above objects, together with other objects to become apparent as the description progresses, are accomplished according to the invention by the provision of a spontaneous breathing apparatus comprising: a source of oxygen containing gas; a catheter in flow communication with the source of oxygen containing gas and adapted to be introduced into a subject""s trachea through a tracheostomy for delivering oxygen containing gas therein; a tracheostomy tube disposed adjacent the catheter and having one end adapted to be disposed in the subject""s trachea; and a pressure actuated threshold valve being connected to another end of the tracheostomy tube, the valve being configured for venting a gas existing within the subject""s trachea at the one end of the tracheostomy tube when the gas exceeds a threshold pressure of the valve, the valve thereby being effective for reducing pressure within the subject""s trachea when the pressure within the subject""s trachea exceeds the threshold pressure.
According to another aspect of the invention, the catheter is a reverse thrust catheter comprising a venturi end adapted to direct a flow of the oxygen containing gas in a direction substantially toward the subject""s glottis.
According to yet another aspect of the invention, the venturi end comprises: a catheter tip defining a plurality of holes therein for allowing the oxygen containing gas to exit from the catheter; and a tubular portion connected to the catheter tip for directing the oxygen containing gas emerging from the holes in the direction substantially toward the subject""s glottis, the tubular portion and an outer circumference of the catheter together defining a venturi gap therebetween.
According to a further aspect of the invention, the venturi gap is approximately 0.025 inch.
According to one aspect of the invention, the catheter is disposed substantially within the tracheostomy tube thereby forming a catheter-tube assembly, the catheter-tube assembly being adapted to be inserted into the subject""s trachea through a single tracheostomy.
According to a further aspect of the invention, the pressure actuated threshold valve is a continuous positive airway pressure valve (continuous positive airway pressure valve).
According the yet another aspect of the invention, the pressure actuated threshold valve includes a sensor therein for sensing an actuation of the valve to release the gas within the subject""s trachea when the pressure within the subject""s trachea exceeds the threshold pressure, the apparatus further comprising an actuator for stopping, or reducing, a flow of the oxygen containing gas from the source of oxygen containing gas into the catheter when the sensor senses an actuation of the valve.
The objects of the invention are further achieved by a method comprising the steps of: providing a source of oxygen containing gas; placing a catheter in flow communication with the source of oxygen containing gas; introducing the catheter into a subject""s trachea through a tracheostomy for delivering oxygen containing gas therein; providing a tracheostomy tube disposed adjacent the catheter; placing one end of the tracheostomy tube in the subject""s trachea; connecting a pressure actuated threshold valve having a gas vent to another end of the tracheostomy tube; and venting, through the valve, a gas existing within the subject""s trachea at the one end of the tracheostomy tube when the gas exceeds a threshold pressure of the valve thereby limiting pressure within the subject""s trachea when the pressure within the subject""s trachea exceeds the threshold pressure.
According to one aspect of the invention, the tracheostomy tube includes a cuff at the one end thereof, the method involving the step of preventing the cuff from inflating during a respiratory cycle of the subject.
A threshold CPAP valve is an important part of the invention, as the apparatus according to the invention mimics a spontaneous form of Airway Pressure Release Ventilation, although its mechanism is different.
The present invention pertains to an apparatus and method suitable for patients with acute or chronic respiratory failure that dispenses with oro-nasotracheal intubation, greatly decreases anatomic dead space ventilation, leads to spontaneous ventilation at small tidal volumes and at low respiratory rates, eliminates the need for tracheal suctioning (cleaning) and greatly decreases the effort of spontaneous breathing, further greatly reducing the need for mechanical ventilation.
The apparatus and method according to the invention are simple and relatively noninvasive, and allow spontaneous breathing in a model of severe acute respiratory failure, without intubation and without adverse effects therefrom, without the need to use a mechanical ventilator, creating a controllable mean airway pressure, facilitating tracheal self cleaning via the RTC, and permitting coughing, eating, drinking and vocalization.